Gas turbine engines conventionally comprise a compressor for pressurizing air to support combustion of fuel to generate a hot gas stream. This hot gas stream drives a turbine connected to the compressor, and is then utilized to obtain a propulsive output or a powered shaft output from the engine. In order to obtain higher operating efficiencies and power outputs, the hot gas stream, when it passes through the turbine, is frequently at a temperature exceeding the physical capabilities of the materials from which the turbines are fabricated, particularly considering the high stresses which are imposed on the turbine rotor. This has led to many proposals for providing cooling systems for the turbine, particularly for those portions exposed to the hot gas stream. Generally, it has been the practice to direct relatively cool air from the engine compressor to the turbine blades, along a path distinct from the hot gas stream, in order to provide the required cooling of the blades. One of the problems which is encountered in such cooling systems, however, is in the mechanism for conveying the cooling air from the compressor to the turbine which is rotating at high speed, and then to the turbine rotor blades themselves.
One system which has been employed to provide air cooling to the turbine blades has involved using a large diameter annular seal somewhat forward to the turbine disk to form a chamber between the annular seal and the disk to receive cooling air from the compressor and convey it to the turbine blades which are mounted on the rim of the turbine disk. Systems of this type, however, are inherently heavy because of the large diameter of the annular seal and are also subject to substantially large air leakage. Other systems have involved the use of annular seals of relatively smaller diameter to form correspondingly smaller annular chambers between the seal and the turbine disk with the cooling air being passed from the smaller annular chamber by means of an impeller mounted on the seal along the surface of the disk to the turbine blades. While systems of this type avoid some of the leakage encountered using the larger annular seals, they are still relatively heavy and require that the annular seal support a relatively large load in the form of the impeller unit.